Insurance Injury Settlement

I was involved in a auto accident 3 years ago in New Jersey. The vehicle did not belong to me. I had a passenger with me. I had just turned 18. I was driving with an expired license. I never went to the hospital nor did I seek a lawyer. 3 years later..age 21 my lower back, neck and shoulder aches every single day. Just recently I started receiving legal documents on behalf of the other party represented by a third party law firm. Need some advice as to what steps I should take regarding this matter. Thank you.